The estimated risk from the observed radon distribu­ tions is such that a substantial fraction of the northeastern United States population is exposed to levels high enough to warrant immediate attention. In recent years, there has been growing concern about homes with high indoor radon concentration levels and a potential for increased risk of lung cancer among occupants of these buildings. Residential buildings measured in the past two years, frequently had radon concentrations 1 to 2 orders of magnitude greater than average.